IEEE Spectrum November, 2014 - 44

members watched the oscilloscope signal change as steel
chairs were moved around the apparatus, minutely alter-
ing the surrounding magnetic fields. The lab's SQUID was
"an extremely sensitive detector of lab chairs," he quipped.
The fruits of their intellectual labors were 25 academic papers
and nine U.S. patents related to SQUIDs and superconduc-
tivity. Even before the team broke up in 1967 or 1968, some
members had already moved on to other topics.
What finally put a stop to Ford's SQUID work, though, was an
internal dispute over who had actually developed the device.
Mercereau had spent much of 1965 and 1966 touting the team's
work at science conferences-so much so that Phil Anderson at
Bell Labs began referring to superconducting quantum inter-
ference as the "Mercereau effect." But within the Ford team,
he was not considered the sole or even the main contributor
to the SQUID's invention. To ease tensions, Jacob E. "Jack"
Goldman, director of the Ford labs, transferred Mercereau to
Aeroneutronic, a lab in Newport Beach, Calif., that had been
purchased by Ford.
The sTory of The sQUId Then Takes a new
direction, with Zimmerman emerging as the
protagonist. Within a year of Mercereau's move
in 1967, Zimmerman also joined Aeroneutronic,
though not to work with his former colleague.
In his new position, Zimmerman led the lab's
cryogenics division and worked on advancing
the RF SQUID toward a marketable product.
He was temperamentally suited to the
task. His varied background included a
stint in Australia during and shortly after
World War II, working on radar and on pho-
tometry. Later, after earning his Ph.D. from
the Carnegie Institute of Technology (now
Carnegie Mellon University) in 1951, he took a
position with the Smithsonian Institution at
the Table Mountain Observatory in California.
There, he worked on measuring the elec-
tromagnetic radiation emitted by the sun,
other wise known as the solar constant, and
he continued that research at the Montezuma Observatory in
Chile's Atacama Desert. The flexibility of mind that allowed
Zimmerman to shift easily from radar to cryogenics to astron-
omy and back to cryogenics would serve him well in his quest
to commercialize the SQUID.
In 1969, while still working for Aeroneutronic, Zimmerman
cofounded-with physicist John Wheatley and several
others-a company in San Diego called Superconduct-
ing Helium Electronics. SHE's main focus was on manu-
facturing RF SQUIDs and the helium-refrigeration units
needed to operate the devices. Initially, the company
sold niobium devices like the ones that Zimmerman had
designed in Dearborn. Eventually, that design evolved into
a niobium-aluminum oxide-niobium device, which was
much easier to make, although it had an inferior signal-to-
noise ratio. SHE's devices were the world's first commer-
cially successful SQUIDs.
| co nti n u e d o n pag e 60

because its current stays constant. Interest-
ingly, the Ford researchers were hesitant about
using the term "SQUID" in official publications,
even though, according to Silver, it soon came
into common use around the lab; he credits
Zimmerman with coining the term.
Thin-film junctions proved very time con-
suming and difficult to reproduce. "Months
would go by when we could not make junc-
tions," Silver later wrote. So Zimmerman
focused instead on making the circuits from
niobium wire, which he happened to have
on hand. Niobium thereafter became the
superconducting element of choice in subsequent SQUIDs
at Ford and elsewhere.
Zimmerman, working with Silver, continued to simplify the
devices, which were still hard to reproduce, in no small part
because niobium is an especially tricky metal to machine.
Finally in 1965 the pair succeeded in making a SQUID con-
sisting of a superconducting ring with just a single Josephson
junction interrupting it. Silver used a 27-megahertz radio -
frequency detection system from his magnetic resonance lab
to measure the SQUID's signals. When an external oscillating
flux was applied to the ring, this low-noise detector captured
the change in the internal flux. The researchers dubbed this
device an RF SQUID. It was cheaper and easier to produce
and became the basis for commercializing the SQUID.
However, as mentioned earlier, the SQUID had nothing to
do with cars, and the Ford team made no serious attempts
to profit from it. Zimmerman would later recount how team
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SPectrUm.ieee.orG

DaviD cohen

Heart of tHe
Matter: Even
after leaving Ford,
Zimmerman [third
from left] continued
to champion the
SQUID. With
biomagnetism
expert David Cohen
[second from left],
he recorded the
first low-noise
magnetocardiogram
in December 1969,
using Cohen's
shielded room at MIT.
Also shown are the
Naval Research Lab's
Edgar Edelsack and a
woman identified only
as "Laurie."
http://SPectrUm.ieee.orG
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